update: 20

Author: hijiangtao

README.md

@@ -23,6 +23,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 | 16 | [3Sum Closest](https://leetcode.com/problems/3sum-closest/) | [JavaScript](./src/3sum-closest/res.js) | Medium |
 | 17 | [Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/) | [JavaScript](./src/letter-combinations-of-a-phone-number/res.js) | Medium |
 | 19 | [Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/) | [JavaScript](./src/remove-nth-node-from-end-of-list/res.js) | Medium |
+| 20 | [valid-parentheses](https://leetcode.com/problems/valid-parentheses/) | [TypeScript](./src/valid-parentheses/res.ts) | Easy |
 | 22 | [Generate Parentheses](https://leetcode.com/problems/generate-parentheses/) | [JavaScript](./src/generate-parentheses/res.js) | Medium |
 | 24 | [swap-nodes-in-pairs](https://leetcode.com/problems/swap-nodes-in-pairs/) | [TypeScript](./src/swap-nodes-in-pairs/res.ts) | Medium |
 | 26 | [Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/) | [JavaScript](./src/remove-duplicates-from-sorted-array/res.js) | Easy |

src/valid-parentheses/res.ts

@@ -0,0 +1,26 @@
+function isValid(s: string): boolean {
+const sLength = s.length;
+if (sLength < 2) {
+return !sLength;
+}
+
+let stack: string[] = [s[0]];
+
+for (let i = 1; i < sLength; i++) {
+const current = s[i];
+if (['{', '(', '['].includes(current)) {
+stack.push(current);
+} else if (['}', ')', ']'].includes(current)) {
+const matchedList = ['{}', '()', '[]'];
+if (matchedList.includes(stack[stack.length-1] + current)) {
+stack.pop();
+} else if (stack.length) {
+break;
+} else {
+stack.push(current);
+}
+}
+}
+
+return stack.length === 0;
+};